There are many reasons why it is important to know the position of a component in an optical system. For example, during assembly of a system or sub-system incorporating a component, it may be important to determine if the component is in the correct position. Similarly, during operation of an optical system, it may be desirable to determine whether a component has moved, or, for a moving component, to determine the position of the moving component. Conventionally, this is be done by attaching a separate opto- or electro-mechanical encoder to the component, which adds size, weight, power, and cost to the system.